The field of the proposed invention relates to a process for improved and cost effective manufacture of noise attenuator parts for electrophotographic printers, copiers, and similar reprographic devices. The invention also applies to parts made with the improved process.
Photoreceptor noise attenuators are well known in the current art for use with drum type photoreceptors, particularly where the electrophotographic system uses a biased charge roller (BCR) to charge the photoreceptor prior to imaging. Without the attenuators, imaging systems that use BCR systems squeak or otherwise emit a high pitch hum which is offensive. The high pitch noise is thought to result from both mechanical vibrations of the hard BCR against the photoreceptor and electrically induced vibrations due to the rapid AC current modulations. It is also believed that the scraping of a cleaning blade against the photoreceptor contributes to noise generation. A number of noise repression techniques are known. However, attenuators of the type disclosed herein offer a simple solution to the noise problem by providing vibration-dampening pressure against the inside diameter of the drum.
Current methods of manufacturing noise attenuators involve a simple extrusion process followed by (1) cutting the extrusion into the desired length, (2) pre-stressing the extruded piece to a specific condition; (3) annealing the extrusion to relieve residual stresses, and (4) machining the extrusion to incorporate a slit and to otherwise trim and finish the attenuator in conformance with its final tolerances. The result of these and other secondary handling and finishing operations is shown in FIG. 1 as a noise attenuator 10 that is made of solid extruded thermoplastic resin, typically PVC. The efficacy of attenuators of the type shown in FIG. 1 is determined primarily by three factors: 1) the intimacy of contact to the inside of the photoreceptor drum; 2) the mass of the attenuator; and 3) the sound dampening characteristics of the attenuator material.
As shown in FIG. 1, sidewall 2 of conventional solid-wall attenuator 10 is typically less than 4 mm thick (more typically around 3 mm) to accommodate the extrusion process. This thickness is limited in practice by several factors, including the probability of sink marks due to thermal shrinkage of thicker parts, longer cycle times due to increased cooling requirements, and an increase in cost as the amount of resin is increased. In FIG. 1, a radius 3 has been extruded during the extrusion process. Gap (or slot) 4 has been cut/routed into the extrusion. After annealing, the combination of the gap 4 and radius 3 operate to provide a spring effect to the attenuator 10 after its insertion inside a drum photoreceptor. Specifically, during assembly, compression forces are applied to attenuator 10 to close gap 4. The stress of these compression forces is absorbed mostly in radius area 3. Once inserted inside the drum, the compression forces are released, and the resin attempts to return to its non-stressed shape. However, the outside diameter of attenuator 10 is sized so that it contacts the inside diameter of the drum prior to gap 4 regaining its entire non-stressed size.
Of critical importance to the design and function of attenuator 10 is that there is substantially zero draft from one end of the attenuator to the other. Such avoidance of draft is critical in order that the attenuator make even and intimate contact with the inside of the photoreceptor drum along the entire length of attenuator 10. When attenuator 10 is made using an extrusion process, then the avoidance of draft is a natural consequence of the manufacturing process.
A practical limitation to the above extrusion process is the speed and efficiency of the process. In addition, any design improvements are limited to the direction of extrusion process or require a secondary operation. For parts made in volumes of millions per year, a more rapid and efficient process would be an injection molding process. Unfortunately, a conventional injection molding process for mass production using multi-cavity molds requires either (1) manufacture of parts with a draft (at least 1-4xc2x0 draft) in order to remove the part from the mold cavity once formed and/or (2) a mold that separates into top and bottom sections along the long dimension of the cavity to free the part for removal. Either of the above characteristics makes a conventional injection molding process undesirable since any draft would need to be machined away and since a mold that separates into top and bottom parts along the long dimension of the part inevitably leaves a mold tracing or mark that also must be machined away.
It would be advantageous to create an efficient injection molding manufacturing process for noise attenuators and other parts without a draft where such process does not require any post-molding finishing. It would also be advantageous to increase the mass of the attenuator or the volume of the attenuator without the major disadvantages associated with such a design and still achieve the required sound dampening characteristics. As described above, the disadvantages include sink marks due to thermal shrinkage (common in thick walled parts over 3-4 mm in thickness), increase in weight, long cycle times and an overall higher cost of the part especially if secondary operations are required to achieve functional performance.
One aspect of the present invention is an improved process for manufacture of components having zero draft sides, comprising: (a) making an injection mold having an end-cap mold section and a cavity mold section that together form a cavity conforming to the zero draft part;
(b) injecting resin material into the mold; (c) foaming the resin material; (d) separating the end-cap section from the cavity section; and (e) removing the part from the mold.
Another aspect of the present invention is an improved zero draft noise attenuator part made by a process, comprising: (a) making an injection mold having an end-cap mold section and a cavity mold section that together conform to the zero draft attenuator part; (b) injecting resin material into the mold; (c) foaming the resin material; (d) separating the end-cap section from the cavity section; and (e) removing the attenuator part from the mold.
Another aspect of the present invention is an improved zero draft cylindrical noise attenuator having a long dimension, comprising: (a) a cylindrical sidewall thicker than 4 mm throughout at least most of its circumference; and (b) a gap along the length of the long dimension.
Yet another aspect of the present invention is an electrostatographic printing engine comprising: (a) an electrostatographic imaging drum; (b) at least one noise attenuator positioned inside the imaging drum wherein the attenuator has a long dimension and comprises: (a) a cylindrical sidewall thicker than 4 mm throughout at least most of its circumference; and (b) a gap along the length of the long dimension.